1. Field of the Invention
The disclosed invention relates to aerogels and specifically to silica aerogels having three-dimensional nanoarchitecture with colloidal gold˜protein superstructures nanoglued therein. The disclosure describes methods for making the composite bioaerogels and their physical and chemical characteristics.
2. Description of Background Art
Much attention has been focused on immobilization of biomolecules in silicate glass formed by the sol-gel method, Eggers et al., Protein Sci. 2001, 10, 250–261. The process involves hydrolyzing an alkoxide to produce a sol, which then undergoes polycondensation to form a gel. Biomolecules are immobilized by being entrapped in the gel during the sol-to-gel transition. The sol-gel materials offer advantages over more traditional organic polymers for biomolecule entrapment in that these materials have increased mechanical strength, chemical stability, biocompatibility, and resistance to microbial attack.
While one can encapsulate a variety of biomolecules (enzymes, proteins, antibodies, cells) in sol-gel-derived matrices, the earliest reported bio/silicate-gels had only 30% activity as prepared using the conventional, alcohol-rich sol-gel preparation. Bioactivity of caged biomolecules rose to 75–95% upon the advent of the Dunn procedure, Dunn et al., Acta Mater. 1998, 46, 737–741, which uses less alcohol and provides better buffering of the sol. Traditionally when biomolecules have been incorporated into sol-gel-derived materials, the resultant gels are either kept wet (forming hydrogels) or are dried from aqueous conditions (forming xerogels) resulting in pore collapse of the material and long-sensing response times. The hydrogels are not ideal for real-world sensing either, in that they must be kept wet, stored at 4° C., and the long-term stability of the encapsulated biomolecule has not been investigated. The longest reported lifetime of these materials is approximately a month when stored at 4° C.
Heme proteins, such as horseradish peroxidase, Bhatia et al., Chem. Mater. 2000, 12, 2434–2441, cytochrome c (cyt. c) Lloyd et al., Langmuir 2000, 16, 9092–9094 and myoglobin, Ellerby et al., Science 1992, 257, 1113–1116, have been extensively studied in sol-gel encapsulation. These proteins retain their spectroscopic properties and chemical functions of oxidation and reduction, ligand binding, or biocatalysis upon encapsulation. In one case, cyt. c was encapsulated into a sol-gel and absorbance-based spectral shifts were used to monitor binding of nitric oxide. Unfortunately, the sensor reaction is reported to have taken two hours to reverse, making dynamic measurements impractical, Aylott et al., Chem Mater. 1997, 9, 2261–2263.